Hello and welcome!
First off, I'm curious as to why you believe you are at high risk for melanoma? I'm asking this because you describe yourself as very dark skinned. Typically, the darker the skin, the less risk one has for developing melanoma and skin cancer in general. The natural pigmentation in the skin offers protection. It is normally those individuals who are fair-skinned, blond/red-haired, with light colored eyes who are most at risk.
Now, this doesn't mean there is no risk whatsoever.
As to moles. Well, moles can develop on any body, regardless of skin color, though they are more prevalent on people with fair skin. Also, it would be the rare person who doesn't have at least one mole somewhere on their body - it might be small, it might be covered by hair, or it might not be easily seen, but there is usually one or more. We are not born with a "set" number of moles, strangely enough. We develop moles continuously through our lifetime. We can also have moles fade and disappear throughout our lifetime. Typically, we gain most of our moles during the span between our 30s - 40s. However, moles can continue to develop throughout our lifetimes.
Moles can be caused through genetics. This might not come directly through our parents, however. It might be a grandparent, or even a great-grandparent. Who knows where those genes might have come from? Moles can also be caused from sun exposure as well. I have a huge number of moles on my shoulders, and that is where I usually suffered my yearly summer sunburns.
How do you stop the progression of moles? If you find that answer to that one, can you let me know?
I'm in my 50s and I still get new moles yearly. Of course, I've had melanoma, so my skin is always changing and doing weird things! You won't be able to stop developing new moles. What you will have to do is monitor them, check for changes and see if anything is out of the ordinary. I also advise everyone to get annual skin checks with a dermatologist - even if they are not at risk of skin cancer! To me, it's the same as getting a yearly physical.
What would be concerning to me are the stripes you mention on your toes. I'm assuming these are on the nailbeds? Hallux, I believe, are bunions? But I may be incorrect, so I'm a bit confused by what you are saying with this. If you are speaking of black stripes on the nail or nailbed, that might be concerning (MIGHT!), and should be checked out. However, this can be a very, very common feature among individuals with dark skin.
I think as long as you stay in touch with your body and do annual skin checks, you should be fine. Listen to your gut - that really is your best indication!